1. Field of the Invention
The present invention relates to an image forming device. More specifically, the present invention relates to an image forming device equipped with a member that presses a thermal head unit.
2. Background Information
Various structures of thermal transfer printers and other image forming devices have been proposed which include a member for pushing a thermal head or print head.
An image forming device is a known example of the thermal transfer printer. FIG. 18 is a perspective view showing the overall structure of a known example of a thermal transfer printer. FIGS. 19 to 21 illustrate the thermal transfer printer shown in FIG. 18 in more detail. This thermal transfer printer will now be described with reference to FIGS. 18 to 21.
As shown in FIGS. 18 to 21, this thermal transfer printer includes a metal chassis 101, an ink ribbon cartridge 102, a take-up reel 103 (see FIGS. 19 and 20), a thermal head unit 104 for executing printing, a platen roller 105 (see FIG. 21) arranged opposite the thermal head unit 104, platen roller bearings 106 configured and arranged to rotatably support the platen roller 105, pressing member 107, a resin drive gear unit 108 for pivoting the pressing member 107 that has a small diameter gear 108a and a large diameter gear 108b, a metal feed roller 109 (see FIG. 19) for feeding printer paper 130, a metal pressing roller 110 (see FIG. 19) arranged to press against the feed roller 109 with a prescribed pressing force, feed roller bearings 111 configured and arranged to rotatably support the feed roller 109, pressing roller bearings 112 (see FIG. 19) configured and arranged to rotatably support the pressing roller 110, bearing support plates 113, a helical coil spring 114 (see FIG. 21), tension coil springs 115, an electric motor 116 (see FIGS. 19 and 20) for driving the feed roller 109 and the take-up reel 103, an electric motor 117 for driving the pressing member 107, a motor bracket 118, a feed roller gear 119 (see FIGS. 19 and 20), a swing gear 120 (see FIGS. 19 and 20), and intermediate gears 121 and 122 (see FIG. 20).
As shown in FIGS. 18 and 19, the motor bracket 118 is mounted to one side panel 101a of the chassis 101. A cartridge insertion hole 101c for inserting the ink ribbon cartridge 102 is formed on the opposite side panel 101b of the chassis 101. Insertion holes 101d for supporting the pressing member 107 are formed on both side panels 101a, 101b of the chassis 101. One end of each tension coil spring 115 is attached to a spring attaching hole 101e provided in the side panels 101a, 101b of the chassis 101.
As shown in FIG. 18, the ink ribbon cartridge 102 has a take-up part 102a and a supply part 102b. A take-up bobbin (not shown) and a supply bobbin 102c (see FIG. 21) are arranged inside the take-up part 102a and the supply part 102b of the ink ribbon cartridge 102, respectively. The ink ribbon 102d is wound onto the take-up bobbin and the supply bobbin 102c. The take-up reel 103 functions to take up the ink ribbon 102d that is wound onto the take-up bobbin and the supply bobbin 102c by engaging with the take-up bobbin. As shown in FIGS. 19 and 20, the gear 103a of the take-up reel 103 is arranged such that it meshes with the take-up bobbin when the swing gear 120 swings. The swing gear 120 is constantly meshed with the feed roller gear 119.
As shown in FIGS. 18, 19, and 21, the thermal head unit 104 has a support shaft 104a, arm parts 104b, and a thermal head 104c. Support holes 104d are formed on the arm parts 104b. As shown in FIGS. 19 and 21, the thermal head unit 104 is mounted within the side panels 101a, 101b of the chassis 101 such that it can pivot about the support shaft 104a. A gap is provided between the support shaft 104a and each support hole 104d for dimensional tolerance. Also, as shown in FIG. 21, the helical coil spring 114 is attached to the support shaft 104a of the thermal head unit 104 on the side of the support shaft 104a close to the side panel 101a of the chassis 101. The helical coil spring 114 functions to urge the thermal head unit 104 in a direction away from the platen roller 105. As shown in FIGS. 18 and 19, bent parts 104e configured to be pressed by the pressing member 107 are provided on the arm parts 104b of the thermal head unit 104. Also, as shown in FIG. 21, the thermal head 104c of the thermal head unit 104 is arranged such that it presses against the platen roller 105 with the printer paper 130 and the ink ribbon 102d in between.
As shown in FIGS. 18 and 19, the pressing member 107 includes a pivot member 107a arranged on the side closer to the side panel 101a of the chassis 101 and having a toothed part 107d, a pivot member 107b arranged on the side closer to the side panel 101b of the chassis 101, and a support rod 107c. Pressing springs 107e configured and arranged to press the bent parts 104e of the thermal head unit 104 are attached to the pivot members 107a and 107b. The pivot members 107a and 107b are attached to the support rod 107c so as not to be relatively rotatable. As shown in FIG. 21, the toothed part 107d of the pivot member 107a on the side near the side panel 101a of the chassis 101 is arranged such that it meshes with the small diameter gear 108a of the drive gear unit 108. The drive gear unit 108 is mounted to the side panel 101a of the chassis 101 and functions to transfer drive force from the electric motor 117 to the toothed part 107d of the pivot member 107a. 
As shown in FIGS. 19 and 20, the feed roller 109 is provided at both ends with bearing support sections 109a each having a smaller shaft diameter than the outermost diameter of the feed roller 109, gear mounting sections 109b, and print paper feeding sections 109c. As shown in FIG. 19, the bearing support sections 109a of the feed roller 109 are rotatably supported by the feed roller bearings 111. As shown in FIGS. 19 and 20, the gear mounting section 109b of the feed roller 109 is inserted into the feed roller gear 119 so as to be relatively unrotatable. Protrusions of a prescribed height are formed by form rolling on the surface of the printer paper feeding sections 109c of the feed roller.
As shown in FIG. 19, the pressing roller 110 is provided with bearing support sections 110a having smaller shaft diameters than the outermost diameter of the rest of the pressing roller 110. The bearing support sections 110a of the pressing roller 110 are rotatably supported on the pressing roller bearings 112. The pressing roller bearings 112 are mounted to the bearing support plates 113, which are provided on the inner sides of the side panels 101a, 101b of the chassis 101. Each of the bearing support plates 113 is mounted to the inner sides of the side panels 101a, 101b of the chassis 101 so as to be pivotable about a fulcrum part 113a. Each of the bearing support plates 113 also has a spring attaching part 113b on which the other end of the respective tension coil spring 115, which urges the pressing roller 110 toward the feed roller 109, is attached. The electric motor 116 is mounted to the motor bracket 118 and serves to drive the feed roller 109 and the take-up reel 103. The driving force of the electric motor 116 is transmitted to the feed roller gear 119 and the gear 103a of the take-up reel 103 through the intermediate gears 121 and 122.
The printing operation of this thermal transfer printer will now be explained with reference to FIGS. 20 and 21. When the electric motor 116 rotates, the motor gear 116a mounted to the shaft of the motor 116 rotates in the direction of the arrow A2 as shown in FIG. 20 and drives the feed roller gear 119 in the direction of the arrow B2 shown in FIG. 20 through the intermediate gears 121 and 122. When the feed roller 109 rotates in the direction of the arrow B2 as shown in FIGS. 20 and 21, the printer paper 130 is fed in the paper feeding direction (direction of the arrow C2 shown in FIG. 21). When this occurs, the swing gear 120 that is swingably coupled to the feed roller gear 119 meshes with the gear 103a of the take-up reel 103 and rotates the gear 103a in the direction of the arrow D2 as shown in FIG. 20.
When the gear 103a rotates in the direction of the arrow D2, the take-up bobbin (not shown), which meshes with the take-up reel 103, rotates and thereby causes the ink ribbon 102d (which is wound onto the take-up bobbin and the supply bobbin 102c) to be taken up. While the printer paper 130 and the ink ribbon 102d are being fed, the drive force of the electric motor 117 is transmitted to the pivot members 107a and 107b of the pressing member 107 through the small diameter gear 108a of the drive gear unit 108, thereby causing the pressing springs 107e to press against the bent parts 104e of the thermal head unit 104. As a result, the thermal head 104c of the thermal head unit 104 presses against the platen roller 105 with the printer paper 130 and the ink ribbon 102d sandwiched therebetween. In this manner, printing takes place.
In the thermal transfer printer shown in FIGS. 18 to 21, the support shafts 104a fit into support holes 104d provided in the arm parts 104b to support the thermal head unit 104 in a pivotable manner, with a gap being provided between the support shaft 104a and each support hole 104d for dimensional tolerance. When the thermal head unit 104 is pivoted, the positioning of the thermal head unit 104 with respect to the platen roller 105 tends to become misaligned due to the gap. As a result, the printing accuracy tends to be compromised.
In view of the above, it will be apparent to those skilled in the art from this disclosure that there exists a need for an improved image forming device that overcomes the problems of the art. This invention addresses this need in the art as well as other needs, which will become apparent to those skilled in the art from this disclosure.